This invention relates generally to electromechanical information storage systems. More particularly, the invention relates to media autochangers used in such systems.
Media Autochangers. Electromechanical information storage systems are commonly used, for example, to create automated libraries for data storage and backup. Many such automated libraries make use of one or more media autochangers, also known as media jukeboxes, to provide large storage capacity relatively inexpensively. In a media autochanger, numerous media units such as discs or tape cartridges can be stored and then independently selected by a picker mechanism for engagement with a drive. Because of the markets into which media autochangers are sold and the environments in which they are employed, it is important to maximize storage density in such systems while minimizing cost as much as possible.
One class of media autochangers seeks to address these concerns by employing a stationary picker assembly in conjunction with a traveling magazine of media units. A typical example of this class of autochangers has the media units mounted on a circular rotating carousel. A control mechanism is used to rotate the carousel until a desired media unit is located adjacent to the stationary picker assembly. The desired media unit is then accessed by the picker mechanism for read or write operations. Carousel designs such as these fail to maximize storage density because the media units in the carousel are necessarily angled relative to one another. This creates angular dead spaces between the media units.
In higher-end products of this class, the picker mechanism is capable of movement in a direction parallel to the carousel""s axis of rotation but not along the arc of rotation. For example, the carousel can rotate about the z axis while the picker moves up or down in the z direction to access stacked discs or cartridges rotating on the carousel. (By way of background, it is believed that the Breece Hill Technologies, Inc. xe2x80x9cSAGUAROxe2x80x9d library and the Exabyte Corporation xe2x80x9c690Dxe2x80x9d library both operate in this manner.) These devices remain within the general class of devices wherein the picker assembly is xe2x80x9cstationary,xe2x80x9d because the picker assembly itself is not capable of movement in the direction of the magazine assembly. These higher-end products not only share the angular dead space problem with their lower-end counterparts, but they also suffer from higher cost associated with providing separate drive mechanisms for the picker and the carousel.
Another class of media autochangers employs a stationary media magazine in conjunction with a traveling picker assembly. In these systems, the media magazine takes the form of a linear array of media slots. In linear designs such as this, the picker assembly moves parallel to the axis of the media slot array from one end to the other in order to access the individual media units mounted therein. (By way of background, it is believed that the ADIC, Inc. xe2x80x9cFastor DLT7xe2x80x9d autochanger operates in this manner.) The benefit of linear designs is that angular dead spaces between media units are inherently eliminated.
End-of-Travel Dead Space. One problem that is common to most of the linear designs is that of dead space on the ends of the picker""s excursion path. A combination of motors, gears, tracks, circuit boards and housings are typically required to implement a picker and to define its excursion path. Consequently, the picker is usually wider than a media slot. In addition, the footprint of the components used to define the excursion path of the picker is usually longer than the length of the media magazine. These factors, either independently or in combination, inevitably impose a minimum on at least one dimension of the autochanger""s enclosure. The result is that dead space occurs between the ends of the media magazine and the walls of the enclosure. For similar reasons, even autochangers of the carousel variety can suffer from the end-of-travel dead space problem if the carousel travels along a finite arc rather than in an endless circle.
It is therefore an object of the invention to enhance the storage density of media autochangers by eliminating end-of-travel dead space.
It is a further object of the invention to eliminate end-of-travel dead space according to a technique that can be applied in autochangers of the linear variety as well as to those of the carousel variety.
The invention includes numerous aspects, each of which contributes to achieving the above and other objects. In one aspect, a magazine assembly containing numerous media units is disposed adjacent to a picker assembly. One of the two assemblies is normally stationary, while the other assembly is a traveling assembly. In either case, the two assemblies cooperate with one another to selectively provide the picker assembly with access to the media units that are stored in the magazine assembly. A motion reversal assembly is coupled to the normally stationary assembly and is engageable by the traveling assembly when the traveling assembly enters an end portion of its excursion path. When the motion reversal assembly is so engaged, it moves the normally stationary assembly in the direction opposite to that of the traveling assembly""s movement. The effect of this movement is an apparent increase in the traveling assembly""s available excursion length. This makes it possible for the picker assembly to access media slots that would otherwise be disposed in the dead spaces located on either end of the traveling assembly""s excursion path.
In media autochangers that employ the invention, additional media slots may be provided in the magazine without increasing the available excursion length of the traveling assembly or the area required to house the device. This achieves enhanced spacial and storage density.